solar charge through a fabric cover
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Forum Name: Podmods, Maintenance, Tips and Tricks
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URL: http://www.rpod-owners.com/forum_posts.asp?TID=15132
Printed Date: 19 Jun 2025 at 4:27pm
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Topic: solar charge through a fabric cover
Posted By: Tulefog
Subject: solar charge through a fabric cover
Date Posted: 02 Feb 2022 at 11:43pm
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I have a 2021 that came with a factory installed solar panel. The solar panel is keeping the dual 12 volt batteries charged fully, even under the ADCO cover I have on the trailer. The cover is made from Tyvek and appears to be woven fabric material, the information says it protects from UV and it is moisture resistant. My last trailer had a solar panel I placed on the roof on top of the cover when I stored it. On that trailer I would unhook the battery cables and just leave the trickle charger leads attached. That avoided parasitic drain from the appliances. I remember taking the battery out and charging it before every trip. I have not taken the rpod out since December, and figured I should fully charge the batteries. The panel on the inside of the trailer said the batteries were fully charged. The panel showed the solar panel charging even with the cover on the trailer. I keep the battery switch off so there is no appliance drain in the trailer when I am not using it. If the solar panel will charge through the cover that will save me going over and fully charging the batteries. My storage lot is about ten miles away, so to remember to go over every month or remove the batteries and bring them home is just one more thing to remember. Is this others experience with solar panels? The cover doesn't block light coming through completely, and from what I can tell the solar panel is working as well as when the cover is off the trailer. I didn't have the tow vehicle hooked up so it wasn't corrupting my observations. Thanks for any input it would be nice to have the batteries charged and always ready to go, but if I am missing something about battery maintenance I want to know. ------------- 2021 Rpod 180 2006 Ridgeline 
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Replies:
Posted By: offgrid
Date Posted: 03 Feb 2022 at 3:17am
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A solar cel/module will produce current in direct proportion to the amount of light it is getting. So of course it will not perform as well when partially obscured as it would in direct sunlight but it won't be zero either. Even on quite cloudy days a rooftop array will get 10% or more of sunny day output.
So pretty clearly you're getting enough charging current from the covered module to keep your battery charged with no load on it. That doesn't take much. Likely you aren't getting enough current to equalize the cells though, which lead acid battery need occasionally, so I would still give it a more agressive charge once in awhile. One thing you might want to do is get a multimeter with clamp on DC current measurement capability. That is very handy to have in your travel toolbox so you can see what your loads are taking and what charging you're actually getting. Be sure to get one that does DC, not just AC current measurements. They are quite inexpensive now on Amazon and other online retail sites. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: Tulefog
Date Posted: 03 Feb 2022 at 6:30pm
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A digital multimeter was not expensive ~$20.00 and has a clamp and rotary selector for AC or DC, I embedded a picture of it. The solar charge coming in now through the cover, going into the batteries may not be enough to charge all the cells equally in each battery and completely charge the batteries? Inadequate charge to a battery's individual cell or cells would be like a low water level in a cell or multiple cells which would show as low total voltage of the battery, if the battery was tested individually. I have two batteries is it possible one battery may be fully charged but the other not and give a full charge readout? To check that I would have to disconnect each battery from the trailer and check the charge in each battery using probes. I there is a way during charging that the batteries can balance their total charges or their individual cells? I believe that is why you are suggesting using a battery charger periodically on each battery to assure all cells are topped off. The multimeter clamp would tell how much charge is going into the batteries and how much is stored in each. Also that would be a good time to make sure all cells are filled above their plates with distilled water. Thank you for your help in understanding this, it will keep me from ruining 12 volt batteries.  ------------- 2021 Rpod 180 2006 Ridgeline
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Posted By: offgrid
Date Posted: 04 Feb 2022 at 3:34am
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Flooded lead acid batteries use a sulfuric acid and water mixture as the electrolyte. Eventually with inactivity the electrolyte will stratify, meaning that the sulfuric acid, which is denser than the water tends to settle to the bottom of the cells, leaving water at the top. That is bad as it can eventually lead to irreversible battery plate damage.
Equalization in flooded lead acid batts involves agessively charging them at a higher than normal voltage for a few hours (around 15V or so). That creates bubbles of hydrogen and oxygen gasses by electrolysis of the water in the batteries. The bubbling mixes the sulfuric acid and water in the cells, reversing the stratification. You can just equalize every month or so and as long as you replace any water that you loose from the charging you won't have any problems from stratification. If that is difficult for you to do and what you're looking for is a way to know when you need to equalize, the best way is to directly test the specific gravity of your battery cells. So rather thann to use a voltmeter which wont tell you anything about the individual battery cells you can buy a battery hydrometer for about $10 which you can use to check the specific gravity at the top of each cell. Higher means more sulfuric acid which means higher state of charge and better mixing. So what you are looking for is a consistent high sg reading. if thats not happening then you need to aggressively charge for a few hours,then recheck. ​Dont check right after adding water as that will give you a false low reading. In your case if you need to equalize it might be enough just to expose the solar module to full sun for a couple of days by temporarily remoing the cover, you might not need to pull the batteries out or plug in the charger. The hydrometer will tell you. For most golf cart type deep cycle batteries an sg of around 1.265 indicates full charge. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: Tulefog
Date Posted: 04 Feb 2022 at 11:59am
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Thank you very much that helps a lot. I have a hydrometer already, and I have just one more question. When using the hydrometer should I take care not to put the hose more than a half inch below the surface of the water/sulfuric acid solution to detect stratification?
I know from work experience not to look directly into the cell and the solution as it is dangerous both gas generation and liquid sulfuric is highly corrosive. Also to get accurate readings on each cell, sample at the same level, so it is tempting to look down in there, but don't, use an inspection mirror. ------------- 2021 Rpod 180 2006 Ridgeline
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Posted By: offgrid
Date Posted: 05 Feb 2022 at 4:52am
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Good question on the level to take the electrolyte from for testing. If you have golf cart batteries I doubt you have enough fluid above the plates to be able to adjust the height much. As long as you are consistent in what you're doing on all the cells I think you should be fine, you're looking for variation cell to cell anyway, not really absolute sg numbers. So it's a matter of getting your technique down and consistent.
Yes battery safety is very important. It's the H2 getting produced that is dangerous, combined with an ignition source which in battery explosions is typically an internal hot spot formed when the battery has current running through it. So shut off all charge sources and loads before opening the batt caps, and give the battery a few minutes for any hydrogen to dissipate, it's much lighter than air so will vent away quickly, a few minutes at most. And by all means wear safety glasses. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: Tulefog
Date Posted: 06 Feb 2022 at 7:58pm
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Thanks for the information, I am going to bring the whole trailer back from storage this week and will check the batteries in place after disconnecting them. Check each cell for specific gravity then adding any distilled water, completely charge and after charging pop the caps after the bubbling stops and check specific gravity by cell again, just to see what happened. Thank you very much for the help. ------------- 2021 Rpod 180 2006 Ridgeline
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